Copolyesters having repeat units derived from succinic acid

ABSTRACT

This invention relates to aliphatic copolyesters prepared from succinic acid (or derivatives thereof) and a process for the preparation thereof. The aliphatic copolyesters contain a second component, 1,4-butanediol, and a third component which is either a diacid or a diol (or derivatives thereof).

This is a divisional application of U.S. application Ser. No. 08/096,752filed on Jul. 22, 1993.

FIELD OF THE INVENTION

This invention relates to succinate copolyesters having repeat unitsderived from succinic acid. These copolyesters are very useful for filmsand injection molding.

BACKGROUND OF THE INVENTION

The preparation of aliphatic copolyesters was reported in the mid-1930'sas described in U.S. Pat. No. 2,012,267. Since that time, there has beena tremendous amount of work done in the field of polyesters. A very highpercentage of this work has been done on aromatic polyesters andcopolyesters, such as poly(ethylene terephthalate) because of their highmelting points, high glass transition temperatures, good barrierproperties, high tensile strengths and other useful properties. Therehas been little commercial interest in aliphatic polyesters because oftheir low melting points and relatively poor physical properties.

The melting temperatures of most linear aliphatic polyesters preparedfrom diacids (or derivatives thereof) and diols are in the range of 50°C.-70° C. Melting temperatures below 80° C.-90° C. are generally notuseful for most commercial applications due to dimensional instabilityupon storage in warm environments.

Two aliphatic polyesters which have unusually high melting temperaturesare poly(tetramethylene succinate) and poly(ethylene succinate). Theirmelting temperatures are 120° C. and 104° C. respectively

While, in general, aromatic polyesters have superior physical propertiesto aliphatic polyesters, aromatic polyesters are not rapidlybiodegradable. Aliphatic polyesters, on the other hand, are generallyconsidered to be rapidly biodegradable. For example, U.S. Pat. No.3,932,319 broadly discloses blends of aliphatic polyesters and naturallyoccurring biodegradable materials. This patent also discloses evidencethat several of the aliphatic polyesters are biodegradable.

Aliphatic polyesters prepared from succinic acid have been claimed assurgical articles as in U.S. Pat. No. 3,883,901. In this patent,succinate polyesters prepared from succinic acid and C2 to C6 diols to a"film- or filament-forming molecular weight" are disclosed. Also,preparation of sutures from both poly(ethylene succinate) andpoly(tetramethylene succinate) are given.

Several other reports of succinate polyesters from medical applicationshave been made. In J. Macromol. Sci. Chem., A25(4), pp. 467-498 (1988)by Albertson and Ljungquist, the preparation of block copolyesters ofpoly(ethylene succinate/poly(tetramethylene glycol) and their use assuture material was reported. In U.S. Pat. No. 4,594,407, thepreparation of polyesters for medical devices from succinic, malic andfumaric acids and 1,4- and 2,3-butanediols was disclosed. U.S. Pat. No.4,032,993 discloses surgical articles prepared from copolyesters ofsuccinic and oxalic acids and various low molecular weight diols.

SUMMARY OF THE INVENTION

This invention relates to a selected group of high molecular weight,high melting, aliphatic copolyesters prepared from succinic acid (orderivatives thereof), 1,4-butanediol, and a third component which iseither a diol or a diacid (or derivatives thereof).

More particularly, this invention relates to aliphatic copolyestershaving an inherent viscosity of about 1.0 to about 2.0 dL/g as measuredat 25° C. in a 60/40 parts by weight solution ofphenol/tetrachloroethane wherein the aliphatic copolyester compriseseither repeat units having the following structure (A): ##STR1## orrepeat units having the following structure (B): ##STR2## wherein R¹ isselected from the group consisting of C2-C12 alkylene, provided thatsaid C₂ -C₁₂ alkylene is other than --(CH₂)₄ --; C4-C12 cycloalkylene;and C4-C12 oxyalkylene; and R² is selected from the group consisting ofC3-C12 alkylene; C4-C12 cycloalkylene; and C2-C12 oxyalkylene.

It is preferred that the copolyester of this invention is essentiallylinear. By the term "essentially linear", it is meant that the weightaverage molecular weight (M_(w)) divided by the number average molecularweight (M_(n)) is less than about 3.0, preferably less than 2.6.

The invention also relates to a process for preparing the high molecularweight aliphatic copolyesters of the invention having good colorcomprising the following steps:

(i) combining aliphatic copolyester forming monomers with atitanium-based catalyst system and phosphorus-based additive,

(ii) in a first stage, heating said reaction mixture between 190° and220° C. at or slightly above atmospheric pressure, and

(iii) in a second stage, heating said reaction mixture between 245° and260° C. under a reduced pressure of less than 2.0 mm of Hg.

Surprisingly, these copolyesters can be converted to film which showvastly superior properties compared to those of poly(tetramethylenesuccinate). In addition, these copolyesters can be injection molded togive flexible parts with unexpectedly high impact strengths andelongations compared to poly(tetramethylene succinate) of similarmolecular weight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1--a graphical representation showing the effect of mole %diethylene glycol on the tangent modulus of succinate copolyester. Itrefers to Example 25.

FIG. 2--a graphical representation showing the elongation of succinatepolyesters. It refers to Example 27.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The succinate polyesters useful in the present invention are random,aliphatic copolyesters having an inherent viscosity of about 1.0 toabout 2.0 dL/g as measured at 25° C. in a 60/40 parts by weight solutionof phenol/tetrachloroethane wherein the aliphatic copolyester compriseseither repeat units having the following structure (A): ##STR3## orrepeat units having the following structure (B): ##STR4## wherein R¹ isselected from the group consisting of C2-C12 alkylene, provided thatsaid C₂ -C₁₂ alkylene is other than --(CH₂)₄ --; C4-C12 cycloalkylene;and C4-C12 oxyalkylene; and R² is selected from the group consisting ofC3-C12 alkylene; C4-C12 cycloalkylene; and C2-C12 oxyalkylene.

As used herein, the term "alkylene" refers to either straight orbranched chain alkyl groups, such as --CH2--CH2--CH2 or--CH2--CH(CH₃)--CH2--, and the term "cycloalkylene" refers to cyclicalkylene groups which may or may not be substituted. The term"oxyalkylene" refers to an alkylene group which contains one to fouroxygen atoms, such as --CH₂ --CH₂ --O--CH₂ --CH₂ --, which also may belinear or branched.

In general, both a diol and a diacid (or derivative thereof) are usedfor making the copolyesters of this invention. When mole percentages arenoted, they refer to a total of 100 mole % for both the diol and diacidcomponents, and do not refer to mole percentages for the total polymer.These diols and diacids (or derivatives thereof) condense to form thebasis of the repeat units of structures (A) and (B).

The copolyesters of this invention can be prepared from succinic acid(or derivatives thereof), 1,4-butanediol, and a third component (eithera diol or diacid). In the case where the third component is derived froma diol [structure (A)], the preferred mole % of R¹ is about 5 to about35 mole % and the mole % derived from 1,4-butanediol is about 65 toabout 95%. In the case where the third component is derived from adiacid or a derivative thereof [structure (B)], the preferred mole % ofR² is about 5 to about 35 mole % and the mole % derived from succinicacid (or a derivative thereof) is about 65 to about 95 mole %. Very lowlevels (up to 5 mole %) of a fourth component [structure (A) or (B)],which can be either a diol or a diacid (or a derivative thereof), arealso useful in these succinate copolyesters. When poly(tetramethylenesuccinate) is modified with less than about 5 mole % of a thirdcomponent [structure (A) or (B)], the elongation is very low. Whenpoly(tetramethylene succinate) is modified with more than about 35 mole% of a third component [structure (A) or (B)], the copolyester losesmost of its crystallinity and is difficult to convert into a usefulfilm.

Where the third and/or fourth component is a diol, preferred diols ofthe invention are ethylene glycol, propylene glycol, 1,3-propanediol,2,2-dimethyl-1,3-propanediol, 1,3-butanediol, 1,5-pentanediol,1,6-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, thiodiethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol,2,2,4,4-tetramethyl-1,3-cyclobutanediol, diethylene glycol, triethyleneglycol, and tetraethylene glycol.

Where the third and/or fourth component is a diacid, preferred diacidsof the invention are glutaric, adipic, pimelic, azelaic, sebacic,fumaric, 2,2-dimethyl glutaric, suberic, 1,3-cyclopentanedicarboxylic,1,4-cyclohexanedicarboxylic, 1,3-cyclohexanedicarboxylic, diglycolic,itaconic, maleic, and 2,5-norbornanedicarboxylic.

The third or fourth components cannot be either 1,4-butanediol and/orsuccinic acid since they are already present.

It is preferred that R¹ of structure (A) and R² of structure (B) ispresent at about 12 to about 30 mole %.

It is more preferred that R¹ is selected from the group consisting ofC2-C6 alkylene, provided that said C₂ -C₆ alkylene is other than--(CH₂)₄ --; C5-C8 cycloalkylene; and C4-C8 oxyalkylene; also it ispreferred that R² is selected from the group consisting of C3-C6alkylene; C5-C8 cycloalkylene; and C2-C12 oxyalkylene.

It is even more preferred that R¹ is selected from the group consistingof C2-C6 alkylene, provided that said C₂ -C₆ alkylene is other than--(CH₂)₄ --; and C4 oxyalkylene; also, it is preferred that R² isselected from the group consisting of C3-C4 alkylene; and C2oxyalkylene.

For the purposes of this invention, examples of alkylene are ethylene,propylene, butylene, hexylene, and decylene. Examples of cycloalkyleneare cyclobutylene, cyclohexylene and cyclodecylene. Examples ofoxyalkylene are oxyethylene, oxypropylene, oxybutylene, oxyhexylene, anddioxyhexylene.

Preferred compositions are poly(tetramethylene succinate-co-glutarate)and poly(tetramethylene succinate-co-adipate) where the mole % derivedfrom the glutarate or adipate is in the range of about 5 to about 35mole % and poly(tetramethylene-co-ethylene succinate),poly(tetramethylene-co-diethylene succinate), andpoly(tetramethylene-co-hexamethylene succinate) wherein the mole %derived from the ethylene glycol, diethylene glycol or 1,6-hexamethyleneglycol is in the range of about 5 to about 35 mole %. More preferredranges for these third components (glycols) would be about 12 to about30 mole %.

It is preferred that the copolyesters of this invention are essentiallylinear. However, these copolyesters can be modified with low levels ofone or more branching agents. A branching agent is defined as a moleculethat has at least three functional groups that can participate in apolyester-forming reaction, such as hydroxyl, carboxylic acid,carboxylic ester, phosphorous-based ester (potentially trifunctional)and anhydride (difunctional).

Typical branching agents useful in the present invention includeglycerol, pentaerythritol, trimellitic anhydride, pyromelliticdianhydride, and tartaric acid (and derivatives thereof).

A preferred range for branching agents in the present invention is fromabout 0.1 to about 2.0 weight %, more preferably about 0.2 to about 1.0weight %, based on the total weight of the polyester.

Addition of branching agents at low levels does not have a significantdetrimental effect on the physical properties and provides additionalmelt strength which can be very useful in film extruding operations.High levels of branching agents incorporated in the copolyesters resultin copolyesters with poor physical properties (e.g., low elongation andlow biodegradation rates). These resulting films and injection moldedarticles from either branched or unbranched succinate copolyesters areuseful in the construction of disposable articles, particularly thosewhich benefit from being biodegradable.

Another type of agent that can be added to increase the melt viscosityof the aliphatic polyesters of the invention is one or moreion-containing monomers.

It is preferred that the ion-containing monomer is selected from thegroup consisting of an alkaline earth metal salt of sulfoisophthalicacid or a derivative thereof. The fourth component of this invention, asdescribed herein, can also be an ion-containing monomer. A typicalexample of this type of agent is sodiosulfoisophthalic acid dimethylester. The preferred weight percentage range for ion-containing monomersis about 0.3 to about 5.0 mole %, preferably about 0.3 to about 3.0 mole%. These ion-containing monomers also increase the melt viscosity of thecopolyester and do not reduce the elongation of the films substantiallyat low levels.

Yet another type of agent that can be added to the reaction involved inthe invention is one or more stabilizers for maintenance of color andmolecular weight.

In the case of succinate copolyesters, phosphorous-containing compoundsare very useful in maintaining color and may improve melt viscosity whenincorporated into the polymer as a trifunctional group. In addition,phenolic-type antioxidants are useful in the present invention.

The copolyesters of this invention can optionally be combined withphosphorous-based compounds which are either an organic phosphite or aphosphonite.

Such compounds may be represented by the formulas ##STR5## where R₁, R₂and R₃ are selected from an aryl radical of 6 to 30 carbon atoms such asphenyl, nonylphenyl, butyl phenyl, butyl methylphenyl, biphenyl andoctylphenyl; and an alkyl radical of 1 to 30 carbon atoms, such asmethyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl, dodecyl,octadecyl, cyclohexyl, isopropyl, isononyl, isooctyl and the like or##STR6## wherein R₃, R₄ and R₅ are as defined for R₁, R₂ and R₃ above.

Examples of these compounds are: tris-(2,4-di-tbutylphenyl)phosphite;tetrakis-(2,4-di-t-butylphenyl)-4,4'-biphenylene phosphite;bis-(2,4-di-t-butylphenyl)pentaerythritol diphosphite;bis-(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite;2,2-methylene-bis(4,6-di-t-butylphenyl)octylphosphite;4,4-butylidene-bis (3-methyl-6-t-butylphenyl-di-tridecyl)phosphite;1,1,3-tris-(2-methyl-4-tridecylphosphite-5-t-butylphenyl)butane;tris-(mixed mono- and nonylphenyl)phosphite;tris-(nonylphenyl)phosphite; and4,4'-iso-propylidene-bis-(phenyl-dialkylphosphite). Preferred compoundsare tris-(2,4-di-t-butylphenyl)phosphite;2,2-methylenebis-(4,6-bi-t-butylphenyl)octylphosphite;bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite, andtetrakis-(2,4-di-t-butylphenyl)-4,4'-biphenylenephosphonite.

In this invention, it is possible to use one of a combination of morethan one type of phosphite or phosphonite compound. The total level forthe presence of each or both of the phosphite and phosphonite is in therange of about 0.05-2.0 weight %, preferably 0.1-1.0 weight %, and morepreferably 0.1-0.5 weight %.

It is possible to use either one such phosphite or phosphonite or acombination of two or more, as long as the total concentration is in therange of 0.05-2.0 weight %, preferably 0.1-1.0 weight %, and morepreferably, 0.1-0.5 weight %.

Particularly preferred phosphites include Weston stabilizers such asWeston 619, a product of General Electric Specialty Chemicals Company,distearyl pentaerythritol diphosphite, having the following structure:##STR7## Ultranox stabilizers such as Ultranox 626, an aromaticphosphite produced by General Electric Specialty Chemicals Company,bis(2,4-di-t-butylphenyl) pentaerythritol diphosphite, having thefollowing structure: ##STR8## and Irgafos 168, an aromatic phosphiteproduced by Ciba-Geigy Corp., having the following structure: ##STR9##Another example of an aromatic phosphite compound useful within thecontext of this invention is Ultranox 633, a General Electric SpecialtyChemical Company developmental compound which is represented by thefollowing structure: ##STR10##

Other commercially available examples of useful aliphatic phosphites areWeston 618 and Weston TSP, both produced by General Electric SpecialtyChemicals Company. Still other commercially available examples of usefulphosphites are Irganox stabilizers such as Irganox 1010 and Irganox MD1024 (N,N'-bis(beta--3,5-di-t-butyl-4-hydroxyphenyl-propiono)hydrazide),both sold by Ciba-Geigy Corp.

Other examples of additives of this type that are useful in thisinvention include phosphoric acid, phosphates, phenolic antioxidants,and ETHANOX antioxidants (available from Ethyl Corp., Baton Rouge, La.).

It is preferred that where the stabilizer is a phosphorus containingstabilizer or a phenolic antioxidant or mixtures thereof, that these beadded in a range of about 0.05 to 0.75 weight % of the total weight ofthe copolyester.

Other additives useful in this invention are inert additives such astalc, clay, TiO₂, CaCO₃, NH₄ Cl, silica, calcium oxide, sodium sulfate,and calcium phosphate. These additives may be present in an amount of0,001-30 weight percent, and more preferably, 0.001 to 15 weightpercent.

The preparation of the aliphatic copolyesters of the invention is wellknown in the art (e.g., U.S. Pat. No. 2,012,267). Such reactions areusually carried out using diols and diacids (or diesters or anhydrides)at temperatures from about 150° C. to about 300° C. in the presence ofpolycondensation catalysts such as titanium tetrachloride, manganesediacetate, antimony oxide, dibutyl tin diacetate, zinc chloride, orcombinations thereof. The catalysts are typically employed in amountsbetween 10 to 1000 ppm, based on total weight of the reactants. Thefinal stages of the reaction is generally conducted under high vacuum(<10 mm of Hg) in order to produce a high molecular weight polyester.

The invention also relates to a process for preparing the high molecularweight aliphatic copolyesters of this invention having good or enhancedcolor properties (i.e., essentially white) and comprising the followingsteps:

(i) combining aliphatic copolyester forming monomers, as describedherein, with a titanium-based catalyst system and phosphorus-basedadditive,

(ii) in a first stage, heating said reaction mixture at from 190° and220° C. at or slightly above atmospheric pressure, and

(iii) in a second stage, heating said reaction mixture between 245° and260° C. under a reduced pressure of 0.05 to 2.00 mm of Hg.

These copolyesters are best prepared with a titanium-based catalystsystem, (e.g. titanium tetraisopropoxide, titanium tetraethoxide,titanium tetrabutoxide, titanium tetrachloride) in the presence of aphosphorus-based additive. The preferred concentration of titanium inthe reaction is about 5 to about 250 ppm, with the most preferredconcentration being about 20 to about 100 ppm. The reaction is bestcarried out in the two stages as described herein.

It is preferred that the said succinate copolyesters be formed by acombination of 1,4-butanediol, succinic acid (or derivative thereof) anda third component, either a dicarboxylic acid (or derivative thereof) ora diol. Said dicarboxylic acids are selected from the group consistingof the following diacids: glutarict adipic, pimelic, azelaic, sebacic,fumaric, 2,2-dimethyl glutaric, suberic, 1,3-cyclo-pentanedicarboxylic,1,4-cyclohexanedicarboxylic, 1,3-cyclohexanedicarboxylic, diglycolic,itaconic, maleic, 2,5-norbornanedicarboxylic, and said diols areselected from the group consisting of ethylene glycol, propylene glycol,1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,3-butanediol,1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,6-hexanediol,thiodiethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol,2,2,4,4-tetramethyl-1,3-cyclobutanediol, diethylene glycol, triethyleneglycol, and tetraethylene glycol.

The copolyester of this invention can be converted to dimensionallystable objects selected from the group consisting of films, fibers,foamed objects and molded objects.

The succinate copolyesters can be converted to thin films by a number ofmethods known to those skilled in the art. For example, thin films canbe formed by dipcoating as described in U.S. Pat. No. 4,372,311, bycompression molding as described in U.S. Pat. No. 4,427,614, by meltextrusion as described in U.S. Pat. No. 4,880,592, and by melt blowing(extrusion through a circular die). Films can be also prepared bysolvent casting. Solvents suitable for dissolving these copolyesters forcasting include methylene chloride, chloroform, other chlorocarbons, andtetrahydrofuran. In addition, it is possible to produce uniaxially andbiaxially oriented films by a melt extrusion process followed byorientation of the film. These succinate copolyesters are preferablyprocessed in a temperature range of 10°-30° C. above their meltingtemperatures. Melting temperatures for these copolyesters range fromapproximately 80°-110° C. Orientation of the films is best conducted inthe range of -10° to 70° C.

Films prepared from these copolyesters have relatively low water vaportransmission rates (WVTR), low moduli (flexible), good elongations (willstretch before breaking) and good tear strengths relative to otherbiodegradable films. Poly(tetramethylene succinate) has a relativelyhigh tangent modulus (Stiff), about 75,000 psi. As the mole percent ofthe third component R¹ or R² increases, the tangent modulus decreasessubstantially and therefore, films made from these copolyesters haveflexibilities near those of commercial polymer films. For example,polyethylene film has a tangent modulus of approximately 10-20,000 psi.The elongation of poly(tetramethylene succinate) is relatively low evenat high molecular weight (IV≃1.2) . However, as the mole percent of thethird component, R¹ or R² is increased, the elongation of films madefrom these copolyesters increases dramatically (inherent viscosity >1.0dL/g) and is comparable to many of the commercial films. The branchedcopolyesters also have useful film properties until the level ofbranching agent exceeds approximately 2.0 wt %. At this point theconcentration of branches becomes high enough that significantelongation is not possible. Thin films produced from these copolyestersmay be used in disposable articles such as food packaging, other typesof packaging materials, trash (garbage or lawn) bags, and agriculturalmulch films. In addition, these thin films are useful as protectivebarrier films in personal care articles such as infant diapers,incontinence briefs, sanitary (feminine hygiene) napkins, tampons ortampon applicators, bed liners or sheets, bandages, and the like. Thesepersonal care articles may be biodegradable. The films generally may beused as a sheet which is impermeable to aqueous-based fluids. They alsomay be used in or for labels, tags, tapes, bottles, and types ofprotective clothing.

The succinate copolyesters can also be injection molded. The molded barsare significantly more flexible and have dramatically higher impactstrengths than poly(tetramethylene succinate). These improved impactstrengths are realized at inherent viscosities less than 1.0 dL/g.Improved elongations are also obtained in the injection molded parts aswith the films, and the improved elongations are again only seen abovewhen the I.V.s are greater than about 1.0 dL/g. In addition, injectionmolded succinate copolyesters will also biodegrade at a much higher ratethan the injection molded poly(tetramethylene succinate) items. Thesuccinate copolyesters can be molded into numerous types of flexibleobjects, such as bottles, pen barrels, toothbrush handles, cotton swabapplicators and razor blade handles.

The succinate copolyesters can also be used to prepare foamed foodservice items. Examples of such items include cups, plates, and foodtrays.

Biodegradable materials, such as the preferred films of this invention,are initially reduced in molecular weight in the environment by theaction of heat, water, air, microbes and other factors. This reductionin molecular weight results in a loss of physical properties (filmstrength) and often in film breakage. Once the molecular weight of thecopolyester is sufficiently low, the monomers and oligomers are thenassimilated by the microbes. In an aerobic environment, these monomersor oligomers are ultimately oxidized to CO₂, H₂ O, and new cell biomass.In an anaerobic environment the monomers or oligomers are ultimatelyoxidized to CO₂, H₂, acetate, methane, and cell biomass. Successfulbiodegradation requires that direct physical contact must be establishedbetween the biodegradable material and the active microbial populationor the enzymes produced by the active microbial population. An activemicrobial population useful for degrading the films and blends of theinvention can generally be obtained from any municipal or industrialwastewater treatment facility or composting facility. Moreover,successful biodegradation requires that certain minimal physical andchemical requirements be met such as suitable pH, temperature, oxygenconcentration, proper nutrients, and moisture level. We have found thatcertain succinic copolyesters are biodegradable in compostingenvironments and hence are particularly useful in the preparation ofbarrier films in disposable articles. We also have found that succiniccopolyesters are more compostable (biodegradable) thanpoly(tetramethylene succinate) as evidenced by a more rapid breakup offilm in a composting environment and by a more rapid loss of molecularweight.

Composting can be defined as the microbial degradation and conversion ofsolid organic waste into soil. One of the key characteristics of compostpiles is that they are self heating; heat is a natural by-product of themetabolic break down of organic matter. Depending upon the size of thepile, or its ability to insulate, the heat can be trapped and cause theinternal temperature to rise. Efficient degradation within compost pilesrelies upon a natural progression or succession of microbial populationsto occur. Initially the microbial population of the compost is dominatedby mesophilic species (optimal growth-temperatures between 20°-45° C).

The process begins with the proliferation of the indigenous mesophilicmicroflora and metabolism of the organic matter. This results in theproduction of large amounts of metabolic heat which raise the internalpile temperatures to approximately 55°-65° C. The higher temperatureacts as a selective pressure which favors the growth of thermophilicspecies on one hand (optimal growth range between 45°-60° C), whileinhibiting the mesophiles on the other.

Although the temperature profiles are often cyclic in nature,alternating between mesophilic and thermophilic populations, municipalcompost facilities attempt to control their operational temperaturesbetween 55°-60° C. in order to obtain optimal degradation rates.Municipal compost units are also typically aerobic processes, whichsupply sufficient oxygen for the metabolic needs of the microorganismspermitting accelerated biodegradation rates.

This invention can be further illustrated by the following examples ofpreferred embodiments thereof, although it will be understood that theseexamples are included merely for purposes of illustration and are notintended to limit the scope of the invention unless otherwisespecifically indicated. The starting materials are commerciallyavailable unless otherwise described. All percentages are by weightunless otherwise described.

EXAMPLES

In the following examples, the tensile strength, elongation at break,and tangent modulus of the films were measured by ASTM method D882; thetear force is measured by ASTM method D1938; the oxygen and water vaportransmission rates are measured by ASTM methods D3985 and F372,respectively. Inherent viscosities are measured at a temperature of 25°C. for a 0.500 gram sample in 100 mL of a 60/40 by weight solution ofphenol/tetrachloroethaneo DSC measurements were made at a scan rate of20° C./min. Molecular weights are measured by gel permeationchromatography and are based on polystyrene equivalent molecularweights.

Abbreviations used herein are as follows: "IV" is inherent viscosity;"g" is gram; "psi" is pounds per square inch; "cc" is cubic centimeter;"m" is meter; "rpm" is revolutions per minute; "BOD" is biochemicaloxygen demand; "vol." or "v" is volume; "wt." is weight; "mm" ismicrometer; "WVTR" is water vapor transmission rate; "rail" is 0,001inch; "Tg" is glass transition temperature; "Tm" is melting temperature;"DEG" is diethylene glycol; "EG is ethylene glycol; "PEG" ispoly(ethylene glycol); "GPC" is gel permeation chromatography; "Mn" isnumber average molecular weight; "Mw" is weight average molecularweight; "Mz" is Z-average molecular weight; "NMR" is nuclear magneticresonance spectroscopy; "DSC" is differential scanning calorimetry.

The composition of the copolyesters is given in brackets following thename. For example, poly-(tetramethylene-co-diethylene succinate) [72/28] refers to a copolyester which was prepared from succinic acid (orderivative) as the only diacid component and 1,4-butanediol anddiethylene glycol as the two diol components. The molar percentages ofthe diol components remaining in the polymer are 72 mol % from1,4-butanediol and 28 mol % from diethylene glycol.

EXAMPLE 1

Preparation of Poly(tetramethylene-co-diethylene succinate) [72/28]

The following materials were charged to a 250 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (0.50 mole)                                                                            59.1   g                                        2.     DEG (0.43 mole)        45.6   g                                        3.     1,4-butanediol (0.57 mol)                                                                            51.5   g                                        4.     Titanium isopropoxide in n-butanol                                                                   0.71   ml                                              solution (1.25 wt/vol % Ti)                                            ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.0 hour, at 210° C. for 1.0 hour, and at220° C. for 1.0 hour. The reaction temperature was then increased to250° C. After stabilizing at 250° C., the internal pressure was reducedto 0.3 mm Hg, and the reaction was continued for 2.0 hrs. The resultingcopolymer was pale yellow and semicrystalline. The analytical data arelisted below:

Inherent Viscosity=1.23 dL/g

DSC data: Tg=-28.2° C.; Tm=91.5° C.

NMR data: 27.7 mol % DEG

GPC data: Mn=64,400; Mw=126,000

EXAMPLE 2

Preparation of Poly(tetramethylene-co-diethylene succinate)[86/14]

The following materials were charged to a 500 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (1.00 mole)                                                                            118.2  g                                        2.     DEG (0.52 mole)        55.1   g                                        3.     1,4-butanediol (1.48 mol)                                                                            133.3  g                                        4.     Titanium isopropoxide in n-butanol                                                                   1.40   mL                                              solution (1.25 wt/vol % Ti)                                            ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.0 hour, at 210° C. for 1.0 hour, and at220° C. for 1.0 hour. The reaction temperature was then increased to245° C. After stabilizing at 245° C., the internal pressure was reducedto 0.3 mm Hg, and the reaction was continued for 2.0 hours. Theresulting copolymer was pale yellow and semicrystalline. The analyticaldata are listed below:

Inherent Viscosity=0.832 dL/g

DSC data: Tg=-25.8° C.; Tm=81.7° C.

NMR data: 14.0 mol % DEG

EXAMPLE 3

Preparation of Poly(tetramethylene-co-diethylene succinate) [71/29]

The following materials were charged to a 250 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (0.50 mole)                                                                            59.1   g                                        2.     DEG (0.46 mole)        48.7   g                                        3.     1,4-butanediol (0.54 mol)                                                                            48.8   g                                        4.     Titanium isopropoxide in n-butanol                                                                   0.71   ml                                              solution (1.25 wt/vol % Ti)                                            ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.0 hour, at 210° C. for 1.0 hour, and at220° C. for 1.0 hour. The reaction temperature was then increased to250° C. After stabilizing at 250° C., the internal pressure was reducedto 0.3 mm Hg, and the reaction was continued for 2.0 hours. Theresulting copolymer was pale yellow and semicrystalline. The analyticaldata are listed below:

Inherent Viscosity=1.46 dL/g

DSC data: Tg=-29.7° C.; Tm=85.1° C.

NMR data: 29.0 mol % DEG

GPC data: Mn=77,800; Mw=151,000

EXAMPLE 4

Preparation of Poly(tetramethylene-co-diethylene succinate)[55/45]

The following materials were charged to a 250 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (0.50 mole)                                                                            59.1   g                                        2.     DEG (0.60 mole)        63.6   g                                        3.     1,4-butanediol (0.40 mol)                                                                            36.1   g                                        4.     Titanium isopropoxide in n-butanol                                                                   0.72   ml                                              solution (1.25 wt/vol % Ti)                                            ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.0 hour, at 210° C. for 1.0 hour, and at220° C. for 1.0 hour. The reaction temperature was then increased to245° C. After stabilizing at 245° C., the internal pressure was reducedto 0.3 mm Hg, and the reaction was continued for 3.0 hours. Theresulting copolymer was pale yellow and amorphous. The analytical dataare listed below:

Inherent Viscosity=1.04 dL/g

DSC data: Tg=-30.0° C.; Tm=None

NMR data: 45.5 mol % DEG

GPC data: Mn=49,500; Mw=95,000

EXAMPLE 5

Preparation of Poly(tetramethylene succinate-co-glutarate)[86/14]

The following materials were charged to a 500 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (0.85 mole)                                                                            100.4  g                                        2.     Dimethyl glutarate (0.15 mole)                                                                       24.0   g                                        3.     1,4-butanediol (2.0 mol)                                                                             180.2  g                                        4.     Titanium isopropoxide in n-butanol                                                                   1.4    mL                                              solution (1.25 wt/vol % Ti)                                            ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.25 hour, and at 210° C. for 1.75 hours.The reaction temperature was then increased to 245° C. After stabilizingat 245° C., the internal pressure was reduced to 0.3 mm Hg, and thereaction was continued for 2.75 hours. The resulting copolymer was paleyellow and semicrystalline. The analytical data are listed below:

Inherent Viscosity=0.908 dL/g

DSC data: Tm=105.5° C.

NMR data: 14.1 mol % glutarate

EXAMPLE 6

Preparation of Poly(tetramethylene succinate-co-glutarate ) [70/30]

The following materials were charged to a 250 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (0.35 mole)                                                                            41.4   g                                        2.     Dimethyl glutarate (0.15 mole)                                                                       24.0   g                                        3.     1,4-butanediol (1.0 mol)                                                                             90.4   g                                        4.     Titanium isopropoxide in n-butanol                                                                   0.71   mL                                              solution (1.25 wt/vol % Ti)                                            ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 190° C. for 1.0 hour, at 200° C. for 1.0 hour, and at210° C. for 1.0 hour. The reaction temperature was then increased to250° C. After stabilizing at 250° C., the internal pressure was reducedto 0.3 mm Hg, and the reaction was continued for 2.0 hours. Theresulting copolymer was pale yellow and semicrystalline. The analyticaldata are listed below:

Inherent Viscosity=1.04 dL/g

DSC data: Tg=-42.1° C.; Tm=86.2° C.

NMR data: 29.7 mol % glutarate

GPC data: Mn=40,700; Mw=91,300;

EXAMPLE 7

Preparation of Poly(tetramethylene-co-ethylene succinate)[83/17]

The following materials were charged to a 500 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (1.0 mole)                                                                             102    g                                        2.     Ethylene glycol (0.90 mol)                                                                           55.8   g                                        3.     1,4-butanediol (1.32 mol)                                                                            118.8  g                                        4.     Titanium isopropoxide in n-butanol                                                                   1.25   mL                                              solution (1.25 wt/vol % Ti)                                            ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.25 hour and at 210° C. for 2.0 hours.The reaction temperature was then increased to 245° C. After stabilizingat 245° C., the internal pressure was reduced to 0.1 mm Hg, and thereaction was continued for 1.2 hours. The resulting copolymer was paleyellow and semicrystalline. The analytical data are listed below:

Inherent Viscosity=1.22 dL/g

DSC data: Tg=-29° C.; Tm=100.3° C.

NMR data: 16.7 mol % ethylene glycol

EXAMPLE 8

Preparation of Poly(tetramethylene-co-ethylene succinate)[83/17]

The following materials were charged to a 500 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (1.0 mole)                                                                             102    g                                        2.     Ethylene glycol (1.20 mol)                                                                           74.4   g                                        3.     1,4-butanediol (0.96 mol)                                                                            86.4   g                                        4.     Titanium isopropoxide in n-butanol                                                                   1.25   mL                                              solution (1.25 wt/vol % Ti)                                            ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.25 hour and at 210° C. for 2.0 hours.The reaction temperature was then increased to 245° C. After stabilizingat 245° C., the internal pressure was reduced to 0.1 mm Hg, and thereaction was continued for 2.5 hours. The resulting copolymer was paleyellow and semicrystalline. The analytical data are listed below:

Inherent Viscosity=1.46 dL/g

DSC data: Tg=-29.3° C.; Tm=81.5° C.

NMR data: 30.4 mol % ethylene glycol

GPC data: Mn=79,000;

EXAMPLE 9

Preparation of Poly(tetramethylene succinate-co-diglycolate)[86/14]

The following materials were charged to a 500 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (0.87 mole)                                                                            102.7  g                                        2.     Diglycolic acid (0.13 mol)                                                                           17.4   g                                        3.     1,4-butanediol (2.0 mol)                                                                             180    g                                        4.     Titanium isopropoxide in n-butanol                                                                   1.40   mL                                              solution (1.25 wt/vol % Ti)                                            ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.0 hour, at 210° C. for 1.0 hour and at220° C. for 1.0 hour. The reaction temperature was then increased to245° C. After stabilizing at 245° C., the internal pressure was reducedto 0.1 mm Hg, and the reaction was continued for 3.0 hours. Theresulting copolymer was light brown and semicrystalline. The analyticaldata are listed below:

Inherent Viscosity=0.742 dL/g

DSC data: Tg=-30.43° C.; Tm=104.5° C.

NMR data: 13.9 mol % diglycolic acid

EXAMPLE 10

Preparation of Poly(tetramethylene-co-hexamethylene succinate)[87/13]

The following materials were charged to a 250 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (0.50 mole)                                                                            59.1   g                                        2.     1,6-hexanediol (0.10 mole)                                                                           11.8   g                                        3.     1,4-butanediol (0.90 mol)                                                                            81.1   g                                        4.     Titanium isopropoxide in n-butanol                                                                   0.87   mL                                              solution (1.25 wt/vol % Ti)                                            ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.0 hour and at 210° C. for 3.0 hours. Thereaction temperature was then increased to 260° C. After stabilizing at260° C., the internal pressure was reduced to 0.2 mm Hg, and thereaction was continued for 3.3 hours. The resulting copolymer was paleyellow and semicrystalline. The analytical data are listed below:

Inherent Viscosity =1,315 dL/g

DSC data: Tg=-33.1° C.; Tm=103.1° C.

NMR data: 13.4 mol % 1,6-hexanediol

GPC data: M_(n) =53,400; Mw=134,000

EXAMPLE 11

Preparation of Poly(tetramethylene succinate-co-adipate)[79/21]

The following materials were charged to a 500 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (0.80 mole)                                                                            94.5   g                                        2.     Adipic acid (0.20 mol) 29.2   g                                        3.     1,4-butanediol (2.0 mol)                                                                             180.0  g                                        4.     Titanium isopropoxide in n-butanol                                                                   0.87   mL                                              solution (1.02 wt/vol % Ti)                                            5.     ULTRANOX 626 (0.1 wt %)                                                                              0.178  g                                        ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.0 hour, at 210° C. for 1.0 hour and at220° C. for 0.5 hour. The reaction temperature was then increased to260° C. After stabilizing at 260° C., the internal pressure was reducedto 0.2 mm Hg, and the reaction was continued for 3.5 hours. Theresulting copolymer was white and semicrystalline. The analytical dataare listed below:

Inherent Viscosity=0.949 dL/g

DSC data: Tg=-39.7° C.; Tm=95.4° C.

NMR data: 21.2 mol % adipate

GPC data: Mn=32,400; Mw=83,400

EXAMPLE 12

Preparation of Poly(tetramethylene succinate)

The following materials were charged to a 500 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (0.50 mole)                                                                            59.1   g                                        2.     1,4-butanediol (1.0 mol)                                                                             90.0   g                                        3.     Titanium isopropoxide in n-butanol                                                                   0.84   mL                                              solution (1.02 wt/vol % Ti)                                            ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.0 hour, at 210° C. for 1.0 hour and at220° C. for 1.0 hour. The reaction temperature was then increased to250° C. After stabilizing at 250° C., the internal pressure was reducedto 0.2 mm Hg, and the reaction was continued for 3.5 hours. Theresulting polymer was pale yellow and semicrystalline. The analyticaldata are listed below:

Inherent Viscosity=1.12 dL/g

DSC data: Tm=120.8° C.

NMR data: Consistent with poly(tetramethylene succinate)

GPC data: Mn=40,000; Mw=101,000

EXAMPLE 13

Preparation of Poly(tetramethylene-co-diethylene succinate)[71/29] with0.5 wt % glycerol

The following materials were charged to a 250 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (0.50 mole)                                                                            59.1   g                                        2.     DEG (0.43 mole)        45.6   g                                        3.     1,4-butanediol (0.57 mol)                                                                            51.5   g                                        4.     Titanium isopropoxide in n-butanol                                                                   0.71   ml                                              solution (1.25 wt/vol % Ti)                                            5.     Glycerol (0.5 wt %)    0.44   g                                        ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.0 hour, at 210° C. for 1.0 hour, and at220° C. for 1.0 hour. The reaction temperature was then increased to250° C. After stabilizing at 250° C., the internal pressure was reducedto 0.3 mm Hg, and the reaction was continued for 2.75 hours. Theresulting copolymer was pale yellow and semicrystalline. The analyticaldata are listed below:

Inherent Viscosity=1.26 dL/g

DSC data: Tg=-28.8° C.; Tm=87.4° C.

NMR data: 28.6 mol % DEG

EXAMPLE 14

Preparation of Poly(tetramethylene-co-diethylene succinate) [71/29] with1.5 wt % glycerol

The following materials were charged to a 250 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (0.50 mole)                                                                            59.1   g                                        2.     DEG (0.43 mole)        45.6   g                                        3.     1,4-butanediol (0.57 mol)                                                                            51.5   g                                        4.     Titanium isopropoxide in n-butanol                                            solution (1.25 wt/vol % Ti)                                                                          0.71   ml                                       5.     Glycerol (1.5 wt %)    1.31   g                                        ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.0 hour, at 210° C. for 1.0 hour, and at220° C. for 1.0 hour. The reaction temperature was then increased to250° C. After stabilizing at 250° C., the internal pressure was reducedto 0.3 mm Hg, and the reaction was continued for 2.0 hours. Theresulting copolymer was pale yellow and semicrystalline. The analyticaldata are listed below:

Inherent Viscosity=1.23 dL/g

DSC data: Tg=-29.1° C.; Tm=85.4° C.

NMR data: 28.5 mol % DEG

GPC data: Mn=32,100; Mw=170,000; Mz/Mn=16.6

EXAMPLE 15

Preparation of Poly(tetramethylene-co-diethylene succinate)[71/29] with0.25 wt % pentaerythritol

The following materials were charged to a 250 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.     Succinic Acid (0.50 mole)                                                                            59.1   g                                        2.     DEG (0.43 mole)        45.6   g                                        3.     1,4-butanediol (0.57 mol)                                                                            51.5   g                                        4.     Titanium isopropoxide in n-butanol                                            solution (1.25 wt/vol % Ti)                                                                          0.71   ml                                       5.     Pentaerythritol (0.25 wt %)                                                                          0.22   g                                        ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.0 hour, at 210° C. for 1.0 hour, and at220° C. for 1.0 hour. The reaction temperature was then increased to250° C. After stabilizing at 250° C., the internal pressure was reducedto 0.1 mm Hg, and the reaction was continued for 1.0 hour. The resultingcopolymer was pale yellow and semicrystalline. The analytical data arelisted below:

Inherent Viscosity=1.39 dL/g

DSC data: Tg=-31.8° C.; Tm=86.2° C.

NMR data: 28.0 mol % DEG

GPC data: Mn=29,000; Mw=149,000; Mz/Mn=15.2

EXAMPLE 16

Preparation of Poly(tetramethylene-co-diethylene succinate)[73/27] with0.2 wt % tartrate

The following materials were charged to a 250 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.    Succinic Acid (0.50 mole)                                                                             59.1   g                                        2.    DEG (0.43 mole)         45.6   g                                        3.    1,4-butanediol (0.57 mol)                                                                             51.5   g                                        4.    Titanium isopropoxide in n-butanol                                                                    0.71   ml                                             solution (1.25 wt/vol % Ti)                                             5.    Dimethyl L-tartrate (0.20 wt %)                                                                       0.18   g                                        ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.0 hour, at 210° C. for 1.0 hour, and at220° C. for 1.0 hour. The reaction temperature was then increased to250° C. After stabilizing at 250° C., the internal pressure was reducedto 0.2 mm Hg, and the reaction was continued for 1.5 hour. The resultingcopolymer was light brown and semicrystalline. The analytical data arelisted below:

Inherent Viscosity=1.36 dL/g

DSC data: Tg=-28.4° C.; Tm=91.5° C.

NMR data: 27.0 mol % DEG

GPC data: Mn=65,000; Mw=147,000; Mz/Mn=4.35

EXAMPLE 17

Preparation of Poly(tetramethylene-co-diethylene succinate)[77/23] with1.7 wt % sodiosulfoisophthalate

The following materials were charged to a 250 mL single-neck flask:

    ______________________________________                                        Materials                 Amounts                                             ______________________________________                                        1.    Succinic Acid (0.982 mole)                                                                            116    g                                        2.    DEG (0.64 mole)         67.8   g                                        3.    1,4-butanediol (1.36 mol)                                                                             122.5  g                                        4.    Titanium isopropoxide in n-butanol                                                                    1.4    mL                                             solution (1.25 wt/vol % Ti)                                             5.    Dimethyl sodiosulfoisophthalate                                                                       5.33   g                                              (1.7 wt %)                                                              ______________________________________                                    

The flask was fitted with a metal stirrer and a nitrogen inlet and wasimmersed in a Belmont metal bath. The mixture was heated with stirringunder nitrogen at 200° C. for 1.0 hour, at 210° C. for 1.0 hour, and at220° C. for 1.0 hour. The reaction temperature was then increased to245° C. After stabilizing at 245° C. the internal pressure was reducedto 0.3 mm Hg, and the reaction was continued for 2.25 hour. Theresulting copolymer was pale yellow and semicrystalline. The analyticaldata are listed below:

Inherent Viscosity=1.019 dL/g

DSC data: Tg=-30.2° C.; Tm=91.4° C.

NMR data: 23.8 mol % DEG

GPC data: Mn=17,600; Mw=48,900; Mz/Mn=4.6

EXAMPLE 18

The following are additional examples of succinate copolyesters whichwere made by procedures similar to that described in Example 1.

    ______________________________________                                        Properties of Copolymers of Poly(tetramethylene Succinate)                               Third                                                              Third      Component I.V.      TM    Tg                                       Component  (Mole %)  (dL/g)    (°C.)                                                                        (°C.)                             ______________________________________                                        DEG        8.5       1.29      110.4 --                                       DEG        11        0.97      107.7 -26.9                                    DEG        19        0.94      99.1  -32.9                                    DEG        24        1.05      97.4  -24.9                                    EG         15        0.98      103.7 -28.1                                    EG         15        1.38      105.4 -26.0                                    EG         20        1.24      96.4  -29.0                                    EG         26        0.96      88.8  -34.0                                    ______________________________________                                    

EXAMPLE 19

The following are additional examples of succinate copolyesters whichwere prepared using low levels of branching agents by procedures similarto Example 13.

    ______________________________________                                        Properties of Branched Succinate Copolyesters                                 Third           Third   Br.                                                   Compo- Branch   Comp.   Ag.   I.V. Tm   Tg    Mz/                             nent   Ag.      Mol %   Wt. % dL/g (°C.)                                                                       (°C.)                                                                        Mn                              ______________________________________                                        DEG    Glycerol 28.2    0.8   1.47 86.0 -31.2 14.3                            DEG    Glycerol 29.3    3.0   1.01 84.1 -26.7 20.4                            EG     Glycerol 29.0    0.3   0.82 87.4 -30.0 5.2                             EG     Glycerol 29.0    0.6   0.77 87.7 -30.0 7.9                             DEG    Penta-   27.8    0.5   --   87.3 -28.7 14.8                                   erythritol                                                             EG     Penta-   27.0    0.2   1.10 90.7 --    34.2                                   erythritol                                                             EG     Dimethyl 26.2    1.0   1.05 88.7 -29.5 6.8                                    Tartrate                                                               ______________________________________                                    

EXAMPLE 20

Blown film from poly(tetramethylene succinate-co-glutarate) [80/20] wasproduced using a laboratory scale blown film line which consisted of aKillion 1.25 inch extruder with a 15:1 gear reducer. The screw was aMaddock mixing type with an L/D of 24 to 1, although a general purposescrew has also been used. Compression ratio for the mixing screw was3.5:1. A 1.21 inch diameter die with a 5 mil die gap was used. The airring was a Killion single-lip, No. 2 type. A variety of conditions arepossible for producing melt blown films from the copolyesters of thisinvention. Temperature set points for the extruders can vary dependingon the level of inert additives, if any, but are generally in the rangeof 10°-30° C. above the melting point of the copolyester. For thisexample, the level of inert additives was approximately 6 wt % (averagediameter of inert particles was less than 10 microns) and all heaterzones were set between 105°-110° C. with a screw rpm of 20 to 25. Thisproduced a measured melt temperature of 101° C., an amperage of 17 amps,and a pressure of 1,200 psi. Superior performance is generally obtainedat the lowest operating temperature possible. Blowing conditions can becharacterized by the blow up ratio (BUR), the ratio of bubble diameterto die diameter which gives an indication of hoop or transversedirection (TD) stretch; and the draw-down ratio (DDR), which is anindication of the axial or machine direction (MD) stretch. The BUR andDDR were 4.0 and 1.4, respectively, in this example. Prior toprocessing, the copolyesters were dried overnight at 50° C. indehumidified air dryers. The physical properties of the film obtainedare in the table below.

    ______________________________________                                                          Machine  Transverse                                         Property of Film  Direction                                                                              Direction                                          ______________________________________                                        Elongation at Break (%)                                                                           283      359                                              Tangent Modulus (psi)                                                                           28,000   24,000                                             Tensile Strength (psi)                                                                           2,260    3,290                                             ______________________________________                                    

EXAMPLE 21

Blown film from poly(tetramethylene-co-ethylene succinate)[85/15] withan I.V. of 1.38 was produced using a laboratory scale blown film line asdescribed in the previous example. Prior to processing, the copolyesterwas dried overnight at 60° C. in dehumidified air dryers. For thisexample, the level of inert additives was approximately 6 wt % (averagediameter of inert particles was less than 10 microns), all heater zoneswere set at 140° C. This produced a measured melt temperature of 110°C., an amperage of 16 amps, and a pressure of 2,200 psi. The physicalproperties of the film obtained are in the table below.

    ______________________________________                                                          Machine  Transverse                                         Property of Film  Direction                                                                              Direction                                          ______________________________________                                        Elongation at Break (%)                                                                           481      341                                              Tangent Modulus (psi)                                                                           39,000   39,000                                             Tensile Strength (psi)                                                                           3,150    4,330                                             ______________________________________                                    

EXAMPLE 22

Blown film from poly(tetramethylene-co-diethylene succinate)[71/29] with0.2 wt % pentaerythritol and an I.V. of 1.10 was produced using alaboratory scale blown film line as described in the previous example.Prior to processing, the copolyester was dried overnight at 60° C. indehumidified air dryers. For this example, the level of inert additiveswas approximately 9 wt % (average diameter of inert particles was lessthan 10 microns), the initial heater zone was at 80° C. and Zones 2-5were set at 90° C. The screw speed was set at 40 rpm. This produced ameasured melt temperature of 85° C., an amperage of 12 amps, and apressure of 2,100 psi. The physical properties of the film obtained arein the table below.

    ______________________________________                                                          Machine  Transverse                                         Property of Film  Direction                                                                              Direction                                          ______________________________________                                        Elongation at Break (%)                                                                           179       51                                              Tangent Modulus (psi)                                                                           29,000   32,000                                             Tensile Strength (psi)                                                                           2,230    1,290                                             ______________________________________                                    

EXAMPLE 23

Films were also solvent cast from a number of these copolyesters. Thepolyesters were dried either under vacuum or by desiccant drying anddissolved in either chloroform or methylene chloride at a concentrationof 10-20 wt %. The films were cast on stainless steel plates and drawndown to approximately 15 mil with a "doctor" blade. The solventevaporated slowly to leave films of approximately 1.5 mil in thickness.Below are some physical properties of solvent cast films.

    ______________________________________                                        Physical Properties of Solvent Cast Films                                     Prepared from Succinate Copolyesters                                                                          Tangent                                                                              Tensile                                Third   Mol    I.V.    Elongation at                                                                          Modulus                                                                              Strength                               Component                                                                             %      (dL/g)  Break (%)                                                                              (psi)  (psi)                                  ______________________________________                                        EG      20     1.24    303      32,000 4,330                                  EG      26     0.96     61      33,000 1,860                                  EG      30     1.46    260      24,000 2,150                                  Glutarate                                                                             30     1.04    211      32,000 2,160                                  ______________________________________                                    

EXAMPLE 24

The following table shows examples of the relationship between inherentviscosity of the succinate copolyester and elongation of thermally castfilms. The elongation of copolyesters substantially increases when theinherent viscosity is greater than about 1.0 dL/g. Elongation of FilmsPrepared from Succinate Copolyesters

    ______________________________________                                                                I.V.    Elongation                                    Third Component                                                                             Mol %     (dL,/g) at Break (%)                                  ______________________________________                                        DEG           14        0.83     9                                            DEG           14        1.57    656                                           DEG           24        1.05    487                                           DEG           28        1.23    616                                           DEG           29        1.46    776                                           DEG           29        1.10    179                                           EG            15        0.98     76                                           EG            15        1.38    481                                           EG            20        1.24    303                                           EG            30        1.46    260                                           1,6-Hexanediol                                                                              13        1.32    313                                           Dimethyl glutarate                                                                          14        0.91     13                                           Dimethyl glutarate                                                                          20        1.06    283                                           Dimethyl glutarate                                                                          30        1.04    211                                           Diglycolic acid                                                                             14        0.74     11                                           ______________________________________                                    

EXAMPLE 25

The following example shows the relationship between the level of thethird component and the tangent modulus. As the level of the thirdcomponent increases, the tangent modulus decreases indicating a moreflexible film. Also, FIG. 1 is a graphical representation showing theeffect of mole % DEG on the tangent modulus.

Tangent Moduli of Succinate Copolyesters

    ______________________________________                                                  Third                 Tangent                                       Third     Component     I.V.    Modulus                                       Component (Mole %)      (dL/g)  (psi)                                         ______________________________________                                        None      0.0           1.12    75,000                                        DEG       8.5           1.29    57,000                                        DEG       14            0.83    51,000                                        DEG       19            0.94    48,000                                        DEG       24            1.05    34,000                                        DEG       28            1.23    27,000                                        DEG       29            1.46    23,000                                        ______________________________________                                    

EXAMPLE 27

The following examples show the dramatic increase in elongation ofthermally cast films that occurs when poly(tetramethylene succinate) ismodified with a third component and the inherent viscosity is greaterthan about 1.0 dL/g. Also, FIG. 2 is a graphical representation showingthe elongation of succinate copolyesters.

Elongation of Succinate Copolyesters

    ______________________________________                                                                      %                                               Third                 I.V.    Elongation                                      Component Mol %       (dL/g)  at Break                                        ______________________________________                                        None       0          1.12     48                                             DEG        8          1.29    188                                             Hexanediol                                                                              13          1.32    313                                             DEG       24          1.05    487                                             Glutarate 14          0.91     13                                             DEG       14          0.83     9                                              DEG       19          0.94     13                                             DEG       28          1.23    616                                             DEG       29          1.46    776                                             ______________________________________                                    

EXAMPLE 28

This example shows how the elongation is affected by the addition ofvarious levels of branching agents to poly(tetramethylene-co-diethylenesuccinate).

    ______________________________________                                        Elongation of Films From Branched Succinate Copolyesters                                                               Elon-                                                             Branch      gation                               Third              Third     Agent       at                                   Com-  Branching    Component (wt.  I.V.  Break                                ponent                                                                              Agent        (Mole %)  %)    (dL/g)                                                                              (%)                                  ______________________________________                                        DEG   Dimethyl Tartrate                                                                          27.1      0.20  1.36  526                                  DEG   Pentaerythritol                                                                            28.0      0.25  1.39  443                                  DEG   Glycerol     28.6      0.50  1.26  442                                  DEG   Glycerol     28.5      1.50  1.23  261                                  DEG   Dimethyl     22.0      1.70  1.02  169                                        Sodiosulfo-                                                                   isophthalate                                                            DEG   Glycerol     29.3      3.00  1.01   7                                   ______________________________________                                    

EXAMPLE 29

In order to assess the biodegradation potential of the test films,small-scale compost units were employed to simulate the active treatmentprocesses found in a municipal solid waste composter. These bench-scaleunits displayed the same key features that distinguish the large-scalemunicipal compost plants. The starting organic waste was formulated tobe representative of that found in municipal solid waste streams: acarbon to nitrogen of 25:1 ratio, a 55% moisture content, a neutral pH,a source of readily degradable organic carbon (e.g. cellulose, protein,simple carbohydrates, and lipids), and had a particle size that allowedgood air flow through the mass. Prior to being placed in a compost unit,all test films were carefully dried and weighed. Test films were mixedwith the compost at the start of an experiment and incubated with thecompost for 15 days. The efficiency of the bench scale compost unitswere determined by monitoring the temperature profiles and dry weightdisappearance of the compost. These bench scale units typically reached60°-65° C. within 8 hours. After 15 days of incubation there wastypically a 40% dry weight loss in the compost. Films were harvestedafter 15 days of incubation and carefully washed, dried, and weighed todetermine weight loss.

    __________________________________________________________________________    Composting Results for Succinate Copolyesters                                                 Weight Loss                                                             Third After              Loss of                                    Third     Component                                                                           Composting                                                                           Mw Before                                                                           Mw After                                                                            Mw                                         Component Mol % (%)    Composting                                                                          Composting                                                                          (%)                                        __________________________________________________________________________    None       0    1.5     53,700                                                                              51,900                                                                             3.4                                        DEG       25    *      170,000                                                                             138,000                                                                             18.8                                       EG        16    *      153,000                                                                             126,000                                                                             17.6                                       DEG (+0.5 26    *      148,000                                                                             125,000                                                                             15.5                                       wt. % glycerol)                                                               Dimethyl Glutarate                                                                      20    *       97,400                                                                              62,600                                                                             35.7**                                     __________________________________________________________________________     *In these cases, the films broke during the experiment due to the             physical, chemical and biological effects of the composting operation.        Therefore, an accurate weight loss could not be determined in these cases     **This composting experiment was run for 30 days.                        

EXAMPLE 30

Succinate copolyesters can also be injection molded. Poly(tetramethylenesuccinate-co-adipate) [76/24]-and poly(tetramethylene-co-hexamethylenesuccinate) [84/16] were injection molded on a Toyo 90-1. Thecopolyesters were dried in a desiccant dryer at 60° C. for 16 hours. Themolding conditions for both compositions are listed below.

MOLDING CONDITIONS:

    ______________________________________                                        MOLDING CONDITIONS:                                                           ______________________________________                                        Open Cycle Time         4 sec                                                 Inject + Hold Time     20 sec                                                 Cooling Time           50 sec                                                 Inject Time             4 sec                                                 Total cycle Time       78 sec                                                 Nozzle Temp.           120° C.                                         Zone 1 Temp.           120° C.                                         Zone 2 Temp.           120° C.                                         Zone 3 Temp.           120° C.                                         Zone 4 Temp.           110° C.                                         Injection Pressure     600 psi                                                Hold Pressure          600 psi                                                Mold Temp.             12° C.                                          Clamping force         90 tons                                                Screw speed            93 rpm                                                 Mode                   Regular                                                Nozzle                 Straight                                               ______________________________________                                    

The succinate copolyesters molded easily to give white flexible bars.The physical properties of the bars are tabulated below.

Molding Properties of Succinate Copolyesters

    ______________________________________                                        Property of              PTSA**   PTHS***                                     Molded Bars   PTS*       [76/24]  [84/16]                                     ______________________________________                                        Elongation at 2.1          15       194                                       Break (%)                                                                     Tensile Strength                                                                            1,510      2,570    3,280                                       (psi)                                                                         Flexural Strength                                                                           3,930      2,730    3,200                                       (psi)                                                                         Flexural Modulus                                                                            117,000    54,000   66,000                                      (psi)                                                                         Izod Impact                                                                   (Notched, 23° C.),                                                     ft-lb/in      0.58       6.79     4.36                                        I.V. (dL/g)   0.61       0.91     0.97                                        Rockwell Hardness                                                                             100        42       65                                        (R Scale)                                                                     ______________________________________                                         *PTS is poly(tetramethylene succinate).                                       **PTSA is poly(tetramethylene succinateco-adipate).                           ***PTHS is poly(tetramethyleneco-hexamethylene succinate).               

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention. Moreover, all patents, patent applications (published orunpublished, foreign or domestic), literature references or otherpublications noted above are incorporated herein by reference for anydisclosure pertinent to the practice of this invention.

We claim:
 1. An aliphatic copolyester comprising repeat units having thestructure (A):. ##STR11## wherein R¹ is selected from the groupconsisting of C2-C12 alkylene, provided that said C₂ -C₁₂ alkylene isother than --(CH₂)₄ --; C4-C12 cycloalkylene; and C4-C12 oxyalkylene,and wherein the mole % of R¹ is from 5 to 35 mole % and further whereina branching agent is used in the polymerization of said copolyester at alevel of from about 0.1 to about 2.0% by weight based on the totalweight of the copolyester.
 2. The aliphatic copolyester of claim 1wherein a branching agent is used in the polymerization of thecopolyester at a level of from about 0.2 to about 1.0% by weight basedon the total weight of the copolyester.
 3. The aliphatic copolyester ofclaim 1 wherein said branching agent is selected from one or more thefollowing: glycerol, pentaerythritol, trimellitic anhydride,pyromellitic dianhydride, and tartaric acid and derivatives thereof. 4.The aliphatic copolyester of claim 2 wherein an ion-containing monomeris copolymerized at a level of from about 0.3 to about 5.0 mole %. 5.The aliphatic copolyester of claim 4 wherein an ion-containing monomeris copolymerized at a level of from about 0.3 to about 3.0 mole %. 6.The aliphatic copolyester of claim 4 wherein said ion-containing monomeris selected from an alkaline earth metal salt of sulfoisophthalic acidor a derivative thereof.
 7. The aliphatic copolyester of claim 2 whereina phosphorous-containing stabilizer or a phenolic antioxidant ormixtures thereof are added in the range of about 0.05 to about 0.75weight % of the total weight of the copolyester.
 8. The aliphaticcopolyester of claim 7 wherein said stabilizer is selected from thegroup consisting of phosphoric acid, a phosphate, a phosphite, and aphenolic antioxidant.
 9. An aliphatic copolyester comprising repeatunits having structure (B): ##STR12## wherein R² is selected from thegroup consisting of C3-C12 alkylene, C4-C12 cycloalkylene; and C2-C12oxyalkylene, and wherein the mole % of R² is from 5 to 35 mole %, andfurther wherein a branching agent is used in the polymerization of saidcopolyester at a level of from about 0.1 to about 2.0% by weight basedon the total weight of said copolyester.
 10. The aliphatic copolyesterof claim 9 wherein a branching agent is used in the polymerization ofthe copolyester at a level of from about 0.2 to about 1.0% by weightbased on the total weight of the copolyester.
 11. The aliphaticcopolyester of claim 10 wherein said branching agent is selected fromone or more the following: glycerol, pentaerythritol, trimelliticanhydride, pyromellitic dianhydride, or tartaric acid and derivativesthereof.
 12. The aliphatic copolyester of claim 3 wherein anion-containing monomer is copolymerized at a level of about 0.3 to about5.0 mole %.
 13. The aliphatic copolyester of claim 12 wherein anion-containing monomer is copolymerized at a level of about 0.3 to about3.0 mole %.
 14. The aliphatic copolyester of claim 12 wherein saidion-containing monomer is selected from an alkaline earth metal salt ofsulfoisophthalic acid or a derivative thereof.
 15. The aliphaticcopolyester of claim 3 wherein a phosphorous-containing stabilizer or aphenolic antioxidant or mixtures thereof are added in the range of about0.05 to about 0.75 weight % of the total weight of the copolyester. 16.The aliphatic copolyester of claim 15 wherein said stabilizer isselected from the group consisting of phosphoric acid, a phosphate, aphosphite, and a phenolic antioxidant.